Blood Clots Linked to Drospirenone Contraceptives

Women, be careful out there.
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A higher risk of venous thrombosis was linked to drospirenone-containing oral contraceptives than with third-generation combined oral contraceptives, Israeli researchers found.
A multivariable analysis, with adjustment for risk factors associated with thrombotic events, found the risk of deep vein thrombosis and pulmonary embolism was more than 40% greater among drospirenone users than among those using third-generation combined oral contraceptives (RR 1.43, 95% CI 1.15 to 1.78), reported Naomi Gronich, MD, of Carmel Medical Center in Tel Aviv, and colleagues in the CMAJ.
Drospirenone, a fourth-generation progestin used in oral contraceptives, was also linked to a 65% increased risk in venous thrombotic events relative to second-generation combined oral contraceptives (RR 1.65, 95% CI 1.02 to 2.65). Independent risk factors for venous thrombotic events among drospirenone users included older age, obesity, and a history of cancer. Also, risk was highest in the first four months of use.
"The reason for this temporal variation in risk has not been studied," the authors noted. "Perhaps a relatively short period is enough to expose susceptible women and to facilitate the thrombotic process."
No increased risk, however, was found for arterial thrombotic events (transient ischemic attack and cerebrovascular accident) when drospirenone was compared with second- and third-generation combined oral contraceptives, they said.
Combined oral contraceptives are a common method of contraception, but they carry a risk of venous and arterial thrombosis. The population-based cohort study was designed to determine whether drugs containing drospirenone were associated with an increase in thrombotic risk relative to the third-generation oral contraceptives.
For the study, the researchers investigated the risk of venous and arterial thrombotic events among 329,995 women (ages 12 to 50) insured by Clalit and listed in its pharmacy medication database. There were 431,223 use episodes during 819,749 years of follow up. This included women for whom at least one combined oral contraceptive had been prescribed from January 2002 to December 2008.
The researchers found the following:
1,017 venous and arterial thrombotic events (24% of all episodes)
359 cases of deep vein thrombosis (35.3%)
159 cases of pulmonary embolism (15.6%)
194 cases of transient ischemic attack (19.1%)
305 cases of cerebrovascular accident (30%)
Although drospirenone-containing drugs were associated with a significantly increased risk of venous thrombotic events, this was not so for arterial thrombotic events, the researchers reported. It is possible, the investigators said, that because drospirenone is an aldosterone antagonist, it decreases blood pressure slightly, which might balance other factors favoring arterial thrombosis.
In recent years, there has been a trend toward decreased use of second- and third-generation drugs, perhaps because drospirenone is promoted as, "causing less weight gain and edema than other oral contraceptives," Gronich noted.
Susan Solymoss, MD, of McGill University in Montreal, commented that the study adds further evidence for a higher relative risk of venous thromboembolism among women taking drospirenone-containing oral contraceptives, relative to either second- or third-generation oral contraceptives. She observed that recent well-designed studies of drospirenone have shown a higher risk of blood clots versus earlier research that did not identify an elevated risk.
Study limitations included the possibility of a confounding indication if physicians preferred to prescribe drospirenone-containing contraceptives to women with a presumed higher risk of venous thromboembolism. Also, with the database system used for the study, it was not possible to verify diagnoses by examining imaging data. The team was also unable to evaluate hospital admissions or acute illnesses as predisposing factors.
The researchers stated it is important to raise awareness of the increased, though small, risk of thromboembolism relative to third-generation, drospirenone-containing contraceptives, particularly among women who are older or obese. They noted that further research is need to explore the risk mechanisms of this drug.